1. Field of the Invention
The present invention relates to hydraulic starters and, more particularly, to an improved hydraulic starter for a gas turbine engine. The improved hydraulic starter of the present invention has a single, one piece shaft and a clutch positioned concentrically about the shaft in a motor cylinder block. The cylinder block is supported by a movable valve plate and an outer bearing.
The present hydraulic starter can be either a fixed displacement or a variable displacement starter. It can be used for gas turbine engines found in aircraft, marine and industrial applications, such as, for example, power generator stations.
Hydraulic starters for gas turbine engines have, heretofore, used a common hydraulic motor that has been modified to include a two piece shaft. The problem with the two piece shaft hydraulic starter is that engine acceleration exerts forces on the connected parts of the starter. These forces will cause the motor cylinder block to separate from the rigid valve plate.
In addition, the two piece shaft construction requires a larger clutch mechanism to engage the two shafts. Accordingly, the prior art starters are heavy in weight and large in size especially in the axial direction. This greater weight and size has been found to adversely affect performance.
2. Description of the Prior Art
Hydraulic starter systems that have a two piece shaft or equivalent, or a clutch or sprag-type clutch mechanism within the air starter, are known in the prior art. For example, U.S. Pat. No. 2,972,911, which issued on Feb. 28, 1961 to E. A. Volk, Jr., et al., entitled Starter and Accessory Drive, provides a turbine starter having planetary gearing connected through an overrunning sprag-type clutch to an engine connecting member. The sprag-type clutch is located within the starter housing, but adjacent the flange of the housing.
Also, U.S. Pat. No. 3,003,313, which issued on Oct. 10, 1961 to D. J. Bunger, entitled Turbine With Axially Moving Plane Of Rotation, provides another turbine motor that has a starter. The motor has an engine-connecting member that is connected to a drive member of the starter by a one-way coupling or overrunning sprag-type clutch. This patent provides a separate turbine shaft and separate helical spline that connects the shaft to the turbine blade.
U.S. Pat. No. 3,413,860, which issued on Dec. 3, 1968 to H. Heckt, entitled Compressed Air Starter Motor Of Rotary Piston Construction For Internal Combustion Engines, provides a compressed air starter motor that has a wedge body overrunning clutch positioned between a gear unit output member and a pinion shaft. In particular, the starter motor includes air driven rotors operatively connected to a drive pinion, an air operated meshing piston, a pinion shaft for mounting the drive pinion, a gear unit output member, a lever operatively connected between the meshing piston and the pinion shaft so that displacement of the meshing piston axially moves the pinion shaft, and a wedge body overrunning clutch positioned between the gear unit output member and the pinion shaft.
U.S. Pat. No. 4,699,095, which issued on Oct. 13, 1987 to J. Klie, et al., entitled Geared Compressed Air Starter, is directed to a gear-type compressed air starter that has a lead rotor, a driven rotor, a hollow shaft, a rotatable and axially displaceable engagement shaft provided in the hollow shaft, and a free-wheeling mechanism that serves to couple together the hollow shaft and engagement shaft. See also, U.S. Pat. No. 3,811,281, which issued on May 21, 1974 to J. A. Wise, et al., entitled Hydraulic Engine Starting Systems.
Lastly, U.S. Pat. No. 2,909,166, which issued on Oct. 20, 1959 to H. E. Cluff, et al., entitled Air Turbine Starter, is directed to an engine starter that has a drive shaft that remains engaged with the rotating structure of the engine and a gear train that drives an overrunning clutch through a first spline mechanism. The overrunning clutch has a second spline mechanism that serves to transmit motion from the clutch to the engine.
These prior art hydraulic starters fail to provide a one piece shaft construction that is incorporated into a motor cylinder block. Further, the prior art hydraulic starters are not as light in weight and as compact as the hydraulic starter of the present invention. Moreover, the prior art hydraulic starters fail to provide the performance achieved by the simple, one piece shaft construction of the present starter that overcomes the possibility of separation that would normally occur during start-up of the engine. Thus, the present hydraulic starter can be used at higher speeds than known prior art hydraulic starters.